Spectral Line Polarization Switched - PLSW

Normally these commands are used only for spectra line observations. The bias angle in POLSWITCH 3 and 4 would usually be set to $>$ 90 (+ for sources with DEC < latitude), in which case averaging the results of POLSWITCH 1 and 3 (or 2 and 4) will correct the Stokes parameter Q (or U) for an instrumental effect. An observation not position switched is begun by typing START PLSW after entering one of the above POLSWITCH modes. The data for each observation are stored as three scans: the first is the calibrated switched spectrum (e.g. North minus East), the second and third are uncalibrated spectra corresponding to the two individual polarization positions (e.g. the second scan is North and the third East). The switching rate is set by the keyword CPER (the polarimeter will switch positions each CPER seconds).

truein

Table 4.8

PLSW Keywords

POLIN

Move polarimeter into optical axis. TEK4023 keyboard will lock up for 75 sec.

POLANGLE (decimal degrees)

Set polarimeter bias angle, if desired.

CPER (seconds)

Set polarimeter switch rate to n seconds (typically 1-few seconds).

POLSWITCH (1,2,3, or 4)

Start polarimeter switching

TMAIN (seconds)

Set total integration time for SCAN (typically 1-few minutes).

NSCAN (integer)

Set number of polarization switched scans to be done consecutively.

truein